This invention relates generally to systems for determining the spatial position of a target and more particularly to systems of such type which are adapted to determine the spatial position of both active and passive targets. Still more particularly, the invention relates to systems adapted to determine the spatial positions and angular orientations of one object having active targets mounted thereto and another object having passive targets mounted thereto.
As is known in the art, systems are available for determining the spatial position and angular orientation of an object. One such system includes passive retro-reflectors as point markers, or targets, affixed to the object and a second system includes active radiating emitters as the affixed point markers, or targets. Both techniques operate by projecting the image of a high contrasting target onto spaced sensors and using mathematical processing to determine the three dimensional coordinates of each one of the point targets. These three dimensional coordinates (i.e., 3D) are then used as discrete points, or may be considered as a set if their geometric arrangement is known, resulting in the determination of the position and angular orientation of the object (i.e., six degrees of freedom: x, y and z positions and pitch, yaw and roll angular orientations) in space relative to a three dimensional coordinate system centered at a preselected point in space, typically at a point fixed relative to the sensors.
Both active and passive targets operate by projecting the image of a high contrasting target onto spaced sensors and use mathematical processing to determine the spatial position of each one of the targets relative to a three dimensional coordinate system the origin of which is at a pre-selected point in space, typically at a point fixed relative to the sensors. The spatial positions of the targets can be used in many applications. For example, several discrete targets can be affixed to points of interest on a human subject. The human subject can then conduct a series of motions while the system determines spatial position data for each of the various targets affixed to the human subject. The data can be graphically displayed and/or collected and stored for use in a multitude of applications. One of the uses for the data is to provide information to medical professionals conducting medical assessments or diagnosis of the subject's movements. Another use for the data collected is to transfer it to a computer animation software package to create movements in an animated character which are comparable to those made by the human subject. In another example, two or more of the targets may be rigidly affixed to an object in a known geometric arrangement. The system then considers the rigidly affixed targets as a set resulting in the determination of the spatial position of the object and, in the case where two targets are used, the vector angle of the object or, in the case where three or more targets are used, the angular orientation of the object. Determining the spatial position and either the vector angle or angular orientation of an object has several uses. For example, a pointing device can be made out of the object whereby the end tip of the pointing device is in a known position relative to the targets. Such a pointing device can be used as a digitizing pointer held by hand as in reverse engineering applications. An operator moves this pointing object to various known places on a manufactured component and the accuracy of the manufacturing processes is determined from analysis of the determined end tip position of the pointing device.
In one emitting target (i.e., active target) system, multiple charge couple device (CCD) sensors are used to detect the energy emitted by the target. A single point target is energized per sensor cycle to emit infrared energy. During each sensor cycle, the emitted energy focused onto the sensor is collected (i.e. integrated) and shifted to the sensor processing circuitry. In order to determine the 3D position of the target, the target must be detected on at least three sensor axes (i.e. to cover a minimum of 3 orthogonal planes). There are many advantages to a system which uses emitting targets including high contrast images being produced on the sensors, control over activation of each of the targets affording positive and automatic target discrimination, and the ability to use high speed linear sensors. These systems, however, are designed to work with only active point targets.
In one retro-reflective target (i.e., passive target) system, an energy source is energized to emit infrared energy in the general direction of the retro-reflective target. Multiple CCD sensors are then used to detect the energy reflected by the target. During each sensor cycle, the reflected energy focused onto the sensor is collected (i.e., integrated) and shifted to the sensor processing circuitry. In order to determine the 3D position of the target, the target must be detected on at least three sensor axes (i.e. to cover a minimum of 3 orthogonal planes). There are many advantages to a retro-reflective target system including the use of wireless targets and the ability to use inexpensive low speed area array sensors. These systems, however, are designed to work with only passive point targets.
In some applications, such as in an image guided surgical procedure where instrument pose is being tracked with respect to the patient, certain surgical instruments have affixed to them active targets and other surgical instruments have affixed to them passive targets. Thus, when the surgeon is performing a procedure during an operation which requires an instrument having passive targets, such instrument, along with its sensors, processor and display are used by the surgeon. Once that procedure is performed and the surgeon requires an instrument having passive targets, such instrument along with its sensors, processors and display are used by the surgeon.